Transvaal 1887 Rare Vurtheim 2d Bisect on Cover to Natal

1887 Vurtheim 2d olive-bistre BISECTED on envelope from Lydenburg to Natal. The bisect tied by neat strike of numeral 13 cancel, Lydenburg cds 26 SEP (date inverted, year omitted) also on front. The bisect appears to have been used to pay the bookpost rate of 1d for the letter which was sent unsealed. Reverse of envelope bears mimeographed advertising as to the sender's regional wagon services. Taxed "2d" upon arrival probably due to the item being re-rated as a letter. F-VF, a very rare genuine commercial usage of such bisect.